1. Field of the Invention
The present invention relates to a process for extracting Natural Gas Liquids (NGLs) from natural gas. The present invention is more particularly directed to a novel process for extracting NGLs from natural gas that is adaptable to new or for retrofit to existing oil and gas processing facilities.
2. Description of the Background Art
Raw natural gas comes from three types of wells: oil wells, gas wells, and condensate wells. Natural gas that comes from oil wells is typically termed ‘associated gas’. This gas can exist separate from oil in the formation (free gas), or dissolved in the crude oil (dissolved gas). Natural gas from gas and condensate wells, in which there is little or no crude oil, is termed ‘non-associated gas’. Gas wells typically produce raw natural gas by itself, while condensate wells produce free natural gas along with a semi-liquid hydrocarbon condensate. Whatever the source of the natural gas, once separated from crude oil (if present) it commonly exists in mixtures with other hydrocarbons; principally ethane, propane, butane, and pentanes and to a lesser extent heavier hydrocarbons. Natural gas as used in this description refers mainly to non-associated gas or a mix of associated and non-associated gas.
Natural Gas Liquids (NGLs) include ethane, propane, butane, iso-butane, and natural gasoline. Natural gasoline is a mixture of hydrocarbons, mostly pentanes and heavier hydrocarbons. Liquefied Petroleum gas (LPG) refers to predominantly propane and butane, either separately or in mixture. The term NGL as used in this specification refers mainly to small quantities of propane, butanes and natural gasoline.
Recent substantial increases in the demand for NGL has spurred demand for new processes of obtaining NGL from natural gas that yield higher recovery levels.
The conventional processes for extracting NGL from natural gas include those based upon cooling and refrigeration, recycled lean oil absorption, cryogenic process, etc. Typical Turbo-Expander (TBX), straight refrigeration, Joule-Thomson valve (JT), and lean oil processes for extracting NGLs are respectively schematically illustrated in FIGS. 1 to 4. Depending upon the pressure and content of the natural gas source, each of these prior art processes or a combination thereof may be employed. In a number of contemporary refining processes, NGLs are broken down into their base components to be useful by liquefaction and cryogenic distillation. Refrigeration for separation is supplied totally or partially by expansion of the natural gas in a Turbo-Expander. In the lean oil absorption process, NGLs are separated by liquefaction and treatment with an absorption medium. In this process, a natural gas stream is contacted with absorption oil and the NGL components are absorbed and thereafter desorbed and recovered. This process requires expensive regeneration facilities to re-circulate the lean oil.
Due to the increasing worldwide demand for NGL, leading to large volumes of natural gas needing to be processed, there is an urgent need in the art to find efficient methods to recover more of the NGLs in a natural gas feed-stream.